text:
Why is the A380's fuselage designed with a flat bottom?
I want to know if there is some explanation for why the A380 bottom is flat instead of the oval shape, just near the wings.

Maybe area rule?

Note that other airliners also have this more or less flat bottom section where landing gear is stored: the Embraer ERJ-145, the A320, ...

Side effect: more space for advertising and branding, without distortion from curvature.

@Criggie no - its because "flat bottomed planes make the rocking world go round"

There are 2 main reasons:

The wing spars run through that area. If you wanted to keep the wing spar within the oval cross-section, you'd have to install the wing much higher on the fuselage which means the wing spar goes through the passenger cabin.

Behind the wing spars, the landing gear is stored. The flat bottom provides more internal space.

Another image showing more detail of the structure:

And presumably the other significant point is that this area isn't pressurised. So I (would assume) that the cabin section is still oval through that cross-section but that this flat area is mostly faring. Without having to withstand the pressurisation you lose the strength requirements that dictate an oval cross-section.

@Peter absolutely. Imagine the complexity of having to incorporate pressure-tight landing gear doors.

For the landing gear, an unpressurized box is set into the fuselage. The top of this box is the main deck floor.

Hobbes' reply has some of the main reasons, but there's some more:
That flat bit is called the "belly fairing", and its functions are:

Avoid some aerodynamically awkward corners that would happen if the wing profile just went straight through the fuselage, with no rounded corners etc. at the intersection. This is particularly useful at the wing trailing edge, to avoid or reduce corrner separation on the wing suction side. This paper shows what that can look like in a generic wing/body configuration, and here's a picture of a design well-known to have an annoying corner separation that could have been prevented with the right kind of fairing/fillet:

And here's a picture of the A350 belly fairing in that region -- The bit above the wing is no doubt built that way to avoid this sort of issue:

Fuselage structure and pressurisation: The fuselage in most passenger aircraft has a circular cross-section because that can deal with pressure differences between the cabin and the outside better. Although it's not usually pressurised around the wing junction below the passenger deck, it's still structurally much easier to just keep using the same circular (kinda elliptic in the case of the A380) sections, and build additional structural elements around it. Of course the wing box and most of the sturcutural wing elements intersect with the tube, but the main fuselage-shaped spars should not be interrupted, as you can see here for example (That's a C919 fuselage mid-section):

As Hobbes has mentioned the whole wing structure needs to stay below the passenger deck, and the A380 has a particularly large and thick wing, so the structure needed to keep the left and right half together is a bit thicker than the space below the passenger deck allows, and the lowest point is the inboard trailing edge -- that's why the belly fairing is so wide and extending below the fuselage in the case of the A380

Also already mentioned by Hobbes: The landing gear. Structurally, it makes sense to attach the gear directly to some of the fuselage spars, and that means that at least the attachment has to be outside the fuselage tube. That takes up space, and that space needs to be smoothly covered by the belly fairing.

You can look at lots of airliner pictures, and they all have some kind of belly fairing, but the A380's is probably the biggest one. That's probably because it has a very long wing chord, a huge wing, and more and bigger landing gears than most other airplanes. Because volume (thus weight) scales with the 3rd power of size, but structural strength only with 2nd power (i.e. cross-section of structural elements), that means it has to be build a bit sturdier and less slender than smaller airplanes. It was also originally planned as the smallest version of a family of aircraft, with one or two versions having longer fuselages -- that makes the belly fairing look even bigger compared to the fuselage.

Great pic of the "Spitfire blend" on the wing root TE!


text:
Why do we monitor N2 speed rather than N1, when starting jet engine?
I've just heard that N2 is the limit when starting jet engine, But I have no idea why it is.
I know that N1 is Low compressor speed, and N2 is high compressor speed.
So what makes high compressor speed more important when starting jet engine?

If it's a turbofan, N2 represents the core engine compressor/turbine spool that is creating the compress/burn/expand energy that drives the fan, and is exposed to the most energy, that is, velocity and heat.
N1, as the fan/free turbine RPM, is effectively just a windmill tacked on to the end of the core, driving the fan at the other end, same as a free-turbine turboprop, except it's a fan instead of a propeller.  You could jam a piece of wood in the fan to stop it from turing, and you could probably still start the core engine and run it at idle.  This is done with routinely with free-turbine turboprops, although not with turbofans.
In a turboprop or turboshaft, the engine core is called the "gas generator" and you have the same thing. You are concerned with the gas generator RPM while starting, where all the energy is being produced, not the free-turbine/propeller, which is just going along for the ride.
If it's a turbojet with no fan but two compressor/turbine spools, it's still the same thing in the end.  The interior spool that has the highest pressure compressor stages and turbine blades closest to the burner has the most critical parameters, so its speed will be part of the starting limitations, while the low pressure spool is helping but just doesn't have to deal with the same energy level and you can be sure that if the N2 is in limits the N1 will be also.

The N2 shaft is the actual jet engine proper, which has one job: turn fuel into thrust directly.  It is akin to the crankshaft on a gas/diesel engine.
The N1 shaft is an extra turbine put in the thrust stream so it can steal thrust and turn it into rotating shaft power.   It is akin to the transmission shaft on a car, or the Power Takeoff on a tractor.
So when you are starting a gas engine you care about crankshaft RPM not transmission RPM.  Same here.

And then, once the engine is running, other equipment somewhere takes N1 shaft rotation and turns it into something valuable:

for a generating plant, electricity
for a helicopter, rotor drive
for an Abrams tank, track motion
for a ship, propellor drive
for a turboprop engine, propellor drive
for a turbofan engine basically the same thing, but with a "compressor style vane" ducted fan, instead of an open propellor.

All correct answers here, N1 is the large fan at the front and suffers the same effects as turbo lag in a car. N2 does the main compression of the air before it enters the multistage combustion chambers and mixed with fuel. This then drives a series of turbines where one or two actually drives the N2 compressors and one drives the N1 fan. With this setup there is inherent lag between N2 stage and the N1 stage.

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text:
Why do pilots move the propeller lever full forward before landing?
Is it because aircraft can get more "instant" power for go-around, with throttle full-forward?
Or is it for protecting the aircraft's engine from high RPM, low PROP stress in case of go-around?

It's both, but mostly the first one.  You need maximum HP for go-around, which means you need the propeller governor regulating RPM at redline when you call for max power.
You could leave the prop control at a cruise RPM setting, but you would have to remember to move the prop RPM to max before the throttle if you have to go around.  Easier to save time and just move the RPM to max while on approach so it's ready when you need it.  On a piston twin, where you need every fraction of a HP from the good engine if an engine quits on a go around, this can mean the difference between making it and not.
If you leave the prop at a low RPM setting and forget about it when you need to go around, and just shove the throttle forward, you will be at max manifold pressure but with RPM limited to the governor setting, and you won't be getting maximum HP for the engine, and there is a possibility of inducing detonation from the extreme "oversquare" operation, oversquare being RPM lower than MP, especially on a supercharged or turbocharged engine (you won't ruin a Contintental O-470 doing that, but shove the throttle on a supercharged R-985 to get redline MP of 36" while leaving the RPM down at, say, 1200, and you'll probably blow a jug or two).

I would slightly reword this, as engine max rpm  is not synonymous for max pwr rpm.

I know what you're getting at, but that generally applies to engines whose redlines are a function of valve train limits, and the engine is able to wind up well beyond the torque peak, so HP drops off toward redline as torque drops off faster than the RPM rise. This doesn't really apply to direct drive a/c engines that are propeller limited, and where the published HP limit is an arbitrary value reached at the published redline.  In racing, the engines will be allowed to wind up past normal redline for more HP, and they will use a shorter prop.

@Jpe61, for a constant speed propeller in practice they are. Given the choice, which you have with a constant speed prop, there is no reason to ever select higher rpm than max power, so the governor will always be set up so that the max selectable rpm is at or below max power rpm of the engine, and is therefore what gives you most available power.

Yes, but as you wrote, "...at or below max power rpm",  latter of which might be the case in which propeller max rpm is the limit, not engine rpm. I know this is probably overly complex for this specific question, but anyway...

@Jpe61 the max power rpm might be actually higher for the engine alone, but for the propulsion system as a whole the max rpm allowed by the governor is the max power rpm.

Well that would be quite obvious, as no higher rpm and thus power cannot be achieved

I haven't been able to find the actual RPM that the HP peak occurs on an engine like an O-320 based on its air-pumping ability (carb size and cam profile mostly), but it's more than the rated HP limit of 2700.  For a direct example, the geared cont GO300 makes 30 HP more than the direct drive version because it spins up to 3200 rpm. instead of 2700., and I believe that other than the gearbox they are exactly the same.

It's the former.
Having your props taking smaller bites of air means that you get faster response from increased throttle, allowing you to reconfigure from landing to missed with less flailing about. There's an additional benefit at lower throttle settings: you get more drag since your prop is the literal opposite of feathered, so if the air it hitting the prop faster than the engine would be pulling it, you get a bit of a free braking effect, which can be useful for landing as well.

When the propeller pitch is set for high rpm (propeller lever full forward), the engine is operating at (or very close to) its maximum power rpm. Therefore if a go around is initiated, the engine will give its best performance.
If the propeller lever was set at a lower rpm, the full power of the engine could not be utilized, as power is simply torque x rpm. For example for horsepower the equation is torque (in lbft) x rpm / 5252.

Adding to your answer, power comes from rate of fuel burned (fuel flow in gal/sec). The more fuel being converted to HP each second, the more power you have. So the higher the rpm the more fuel-air mixture is going through the engine (engine displacement in cubic inches times 1/4 RPM for 4-cycle engine).

@CharlesBretana not really. Fuel burned equates to energy, not output power. Some energy is lost (heat) and some arrives at the crankshaft output. If there is no torque on the shaft, there is no output power, just losses. For instance a car engine with gear in neutral does not produce power. Increase the fuel, the RPM goes up untill losses equals fuel burned. Clutch the engine, a torque is produced, together with the RPM there is now an effective output power. Torque is merely the balance between effort  (pressure on top of the pistons) and resistance (propellor on a plane).

@Tim, please read more carefully (no offense (grin)), but I said Rate of fuel burned, not quantity. I included the parenthetical (fuel flow in gal/sec) to make that as clear as possible. But you are right that fuel quantity equates to energy...

To be absolutely specific, the energy content of the fuel burned is related to the quantity of the fuel in mass, not volume

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text:
How heavy are turbofan and turboprop propeller blades?
How heavy are the blades from

Turbofan (CFM56-5B, RRTrent800, PW4062A) and
Turboprop (PW127M)

engines?
Is there a general appromixation like
$$ m_\mathrm{Fan} = 0.1 \times m_\mathrm{Turbine} $$
as well?

If you are searching for open source data, you may ask on opendata.SE

According to this ATSB Australia Report, the Original Blade Weight of the Trent 800 Blade that failed was 11.6KG. The weight of the blade in grammes is etched into the blade root.
https://www.atsb.gov.au/media/33974/tr200100445_001.pdf Page 9/10.
Fan Blades of the same type all differ (slightly) in weight and are chosen specially to balance the engine when it rotates, or balance weights are added to the blade much like your wheel on your car. This is to avoid vibration.


text:
Can a Private pilot fly a company aircraft for business purposes if he is not being paid?
I understand that if you are carrying passengers and getting paid, then you have to have a commercial license.
What about this scenario? I have a PPL (Private Pilot License).  My friend owns a company that owns a plane.  If I fly him and/or his employees around, and am not being paid for the time and just doing out of the goodness of my heart, is that okay?

In the scenario you're wondering about, who is paying for the expenses of the flight: you, or your friend (and/or his company)? Also, are you logging the time that you spend flying or not?

PPL by Private Pilot License?

Which country or regulations are you asking about?

USA.  they would be paying for all plane expenses.  Im assuming that if I log time that would make a difference.  Let's say I wasn't and only getting the "experience" time from it.

"PPL by Private Pilot License? " not sure I understand question.  Standard single engine private pilots license in the US is what I would have.

@Itza Zkrit Sorry, I was momentarily confused for a sec of what PPL meant.

The FAA has a wide definition of "compensation", even logging hours can be considered compensation.

@Itza Zkrit, be careful and don't assume that logging or not logging time makes any difference.  CFR 61.113 uses the term "act as pilot in command".  If you are the only qualified pilot in the airplane then that is you...  Please see my answer on the subject and let me know if you have any questions.

I'd say you'd be on thin ice with this. The principle is that private pilots cannot be compensated for their flying, with very few exceptions. That doesn't necessarily mean getting paid to fly, it can mean having the expenses of the flight given to you in some way.
Say you take 3 friends on a trip, and your friends pay all the costs. You'd be in violation of FAR 61.113 because you haven't paid your share, in other words you've received compensation. You need to pay 1/4 of the costs of the trip.
In another case you are going on a business trip and decide to fly yourself and your employer pays all the expenses. This is legit because flying is incidental and not the purpose of the trip.
In the case you are stating you have no reason to be flying the airplane other than the flight itself, therefore flying for free means you are receiving compensation and a violation of FAR 61.113.
Note other countries may vary, the UK is extremely similar to the US on this, as are most European countries, I can't speak for anywhere else.

The answer depends on the reason why you are flying your friend and his employees around.  You don’t state whether or not your friend employs you in his company, but from the wording of your question I would guess that is not the case.
IF you were employed by your friend, and IF the flight was “only incidental to that business or employment, AND the aircraft does not carry passengers or property for compensation or hire” then you may act as pilot in command AND receive compensation.  61.113(b), (1) & (2)  This is the only scenario where a Private Pilot may actually be compensated.
However, if you are flying them around for fun, “out of the goodness of your heart”, then you would fall under 61.113(c) and would need to “not pay less than the pro rata share of the operating expenses.”
Don’t mix the subsections of 61.113 together, they describe distinctly different scenarios.  Being the recipient of free flight time is not the same thing as being compensated to fly.  Reference subsections (d) and (e).
For example, the Civil Air Patrol has many members with a PPL who join not only out of a sense of Civic duty, but to be able to fly without the costs of renting or owning an airplane. They are not compensated for their volunteer service, but if they are flying a CAP funded mission they receive free flight time.

The privelages of a CPL are it allows you to fly an aircraft CARRYING PASSENGERS OR PROPERTY FOR COMPENSATION OR HIRE under specific circumstances governed under 119.1 of the FARs.  The FARs do, however, allow a private pilot to fly for compensation or hire, only if the flight is incidental to the pilot’s employment and it does not carry passengers or property for compensation or hire.  See FAR 61.113.
The other requirement here is that you the pilot are required to pay no less than a pro rata share of the aircraft’s operating expenses eg fuel, oil, parking fees, etc.
Be careful, as well, to conform with the terms of AC 120-12 when discussing this in order to comply with the FAA’s rules concerning holding out for common carriage, as this can get you into trouble very quick if you don’t

Everything you've said is 100% correct.  I worry that the OP might still find it confusing simply because of the amount of specialized terminology that one needs to use when talking about this particular topic.

@SteveV. To amplify the point he made, a pilot with a commercial certificate may be hired to fly the company plane but a private pilot may not. In that case the commercial pilot may receive compensation and the company can pay all of the expenses. If the person works for the company and has a reason to be at the meeting—and not just to fly the people there—then they can fly the company plane and receive their normal compensation for working that day. The company can pick up expenses of the flight. It gets trickier if the pilot flies their own plane but can still be done if you follow the regs.


text:
Can actual instrument time count as simulated instrument time for the PPL?
Just wondering if actual instrument time can be added with simulated instrument time for the requirements of the Private Pilot minimums (3 hour instrument). I have actual instrument time from when my CFI showed me what it was like to fly in clouds. (USA)

Yes.
The requirements for a private certificate are stated in 14 CFR 61.109(a)(3) as “flight training ... instrument flight”.
In 14 CFR 61.1, Instrument training is defined as:
Instrument training means that time in which instrument training is received from an authorized instructor under actual or simulated instrument conditions.

Provided your CFI and you were flying on a filed and ATC cleared IFR flight plan at the time of the real instrument time was acquired, then yes, you can use that instrument time toward your PPL Aeronautical Experience requirements.  It does not necessarily need to be done under the hood. 61.109(a)(3) just requires the applicant log 3 hours of dual instruction time flying solely on reference to the instruments, whether simulated or real IMC conditions.
The downside here is that unless you did the dual instrument time with a CFII, you cannot use that time toward an instrument rating or advanced pilot or flight instructor certificates per 61.109.

Just to be clear - the flight instructor must only have an instrument rating (duh), but need not be a CFII. Also, yes, you can get in trouble if not on a flight plan or IFR clearance, but actual can be logged in rare circumstances where fight by sole reference to instruments is necessary... so almost but not quite on this answer.

No the flight instructor must hold a commercial pilot certificate in the airplane category and class used for instruction here with an instrument rating AND must hold a flight instructor certificate in the airplane category and class used here for instruction along with a separate instrument rating on the flight instructor certificate (CFII) in order for you to log actual IMC time during instruction.

ever think about how they give flight training in Seattle with the 80% of the days being rainy and overcast? A CFI may conduct any flight training under IFR toward a private certificate or commercial or CFI, but may not train students for an instrument rating or CFII. ALMOST EVERY TRAINING FLIGHT IN THAT PART OF THE COUNTRY INCLUDES AN INSTRUMENT APPROACH.

It appears as though you are correct, at least for training toward a PPL.  The downside is that if the student wanted to proceed with instrument training toward an instrument rating, they would not be able to use that accrued time toward the rating unless the instructor was a CFII.  Nor could it be used toward CPL or ATPL.  Also in the case of Seattle, most training flights get cancelled there or they simply wait for VFR weather minimums to conduct the flight in, which does happen there, even in winter time.  Very rarely are instrument approaches conducted as part of primary flight training.


text:
What is the naming convention for European airways?
I know that in the U.S. low altitude airways are called Victor (below 18.000ft, e.g. V123) and high altitude routes are called Jet (above 18.000ft,e.g. J123). Can somebody explain the European airspace routes naming? Thanks!

In the US there are also ATS routes Q and T. For EU routes, this document for Jeppesen may help. In general EU is closer to ICAO recommendations.

US V/J routes are based on VORs. There are also A (Amber), B (Blue), G (Green) and R (Red) routes based on NDBs, but AFAIK only one (in NC) remains outside AK. Based on the answers below, the US uses a valid subset of ICAO rules, so you don't have to learn two incompatible systems (as is often the case with the US).

ATS routes in Europe are designated just like the rest of the world. ICAO publishes guidelines for the designation of ATS routes in Annex 11, which are adopted by almost all countries.
A route will consist of a possible prefix (see below) a letter (see below) and a basic designator (a number between 1-999).
The three types of prefix are:
K (Kopter) to indicate a low-level helicopter route
U to indicate an upper route, available only in upper airspace
or S to indicate a route only used by supersonic aircraft (not very common).
The letters can be:
A, B, G, R for regional routes which are not RNAV routes
L, M, N, P for regional RNAV routes
H, J, V, W for non-regional non-RNAV routes
Q, T, Y, Z for non-regional RNAV routes
In addition, states may add the letters F or G to the end of a route to indicate that the route is in class F or G airspace respectively. To my knowledge, this is not very common (and most ATS routes are in controlled airspace anyway).
Examples:
KY80 ("Kopter Yankee 8-0)
UN872 ("Upper November 8-7-2)
T54 ("Tango 54")


text:
Is there any source of live ATC audio with subtitles?
I'd like to know if there is a way to hear ATC and pilots' communications, with subtitles.

With subtitles?   Who do you think could possibly add that much text to live audio??

I mean automatic subtitles such as the youtube subtitles option

I removed your second question completely: please ask only one question at a time. If you haven't already seen the [tour] it might be helpful to understand how this site works.

Not an answer, but if your goal is to understand what you're hearing then you don't need live audio to do that. You can listen to any ATC recordings with subtitles and use them to 'practice' and then eventually listen to live audio. Some subtitles may not be completely accurate but that's probably always going to be an issue, whether the audio is live or not.

A service that used automatic speech recognition to transcribe live ATC feeds could be useful for people with poor/no hearing.

Is there any way to authoritatively answer this question in the negative? My strong suspicion is that there are no such sites, based on (1) nobody being aware of one, (2) the very limited utility & high technical difficulty in implementing such a service, for a very slight audience within what is already a "niche" field. But can I say with certainty that there are none, at all, anywhere? Nope... no more than I can prove Bigfoot doesn't exist.

@RalphJ https://xkcd.com/1235/

Not live with subtitles, but there are certainly plenty of ATC/pilot recordings on youtube
https://www.youtube.com/results?search_query=atc+conversations
Plus Live ATC streams. I can't access these (lousy cell phone coverage), give them a try.
https://www.liveatc.net/topfeeds.php

+1 Some of the ATC recordings on YouTube come with on-screen captioning and/or diagrams to help the viewer make sense of the events in the video.

I don't know if the question was edited after your answer, but they're asking for live ATC audio with subtitles, which none of your links provide.

Live captioning does not exist that I am aware of.  Live captioning is also not needed to get used to the conversation flow. Recorded with captioning will do.

Might be worth linking to the Android and iPhone apps for LiveATC: https://play.google.com/store/apps/details?id=net.liveatc.liveatc_app&hl=en_US  https://itunes.apple.com/us/app/liveatc-air-radio/id317809458?mt=8

If you want an easy way to read the standard communications rather than listening to them, the US National Transportation Safety Board (NTSB.GOV) reports have written Voice Cockpit Recorder (VCR) transcriptions at the end of the Report in an Appendix.
That will include communications with Towers, Centers, and other Aircraft. This is because the NTSB is legally prevented from releasing the audio recovered from the VCR. Recordings made from popular shows like "Maday" or "Air Disasters" are made by actors performing the written transcript and are not the the voices you would hear on the actual recorder from a given event.
This CVR Handbook PDF explains how the data can be used by the NTSB.
Because this is a law, and specifically covered by that law is the reason why it cannot be requested via a Freedom of Information Act (FOIA) requests, unlike more mundane 911 calls.

Note that you can request radar replays and ground-recorded audio from the FAA for any given flight on any given day. These data will include all radio transmissions captured at the control position as well as controller-to-controller "landline" coordination. They are stored for some length of time, possibly 45 days or possibly much longer (the low-bandwidth audio recordings don't take up that much space). Recordings associated with an aircraft accident are kept indefinitely (I believe) but those may in fact be un-FOIA-able—I'm not sure.

@randomhead I made specific reference to the CVR in my answer because those have transcripts that the OP wanted to see. They were not asking for audio recordings. Please read the post before making unrelated comments about the topic of my answer. CVR transcripts are professionally prepared and will not have the same errors that auto generated "Closed captioning" style solutions will contain based on word strings not in common every day non-airline use.

If OP is asking for recordings with subtitles then your answer is just as useless as my comment on it.


text:
Are there examples of passengers' Micro SD cards or USB flash drives surviving crashes?
Are there any well-documented cases of Micro SD cards or USB flash drives surviving 100% hull loss crashes? I'm asking about cards held by passengers, not ones that are part of the aircraft's systems.

are you asking for flash storage from PAX or from crew/avionics?

@selectstriker2: from PAX

The SIM cards would survive almost any crash unless they end up in fire or get crushed via some other article. The reason is that they have little mass and are really small.

@GürkanÇetin: Of course, "end up in fire" and "crushed" are rather common outcomes for things involved in an aircraft crash...

Yes. Some videos where recovered from the germanwings crash. See this article talking about it: link
The video can now easily be found online. I recommend against it tho.


text:
What does "Controlling Object" mean in FAA documentation?
I was examining FAA's legacy files, which contain information for various airspace elements, and I noticed that there is a field in the airport layout file called "Controlling Object", for both base and reciprocal ends of the runway.
Some of its properties:

Controlling object description
Controlling object marked/lighted
FAA CFR Part 77 runway category
Controlling obstacle clearance slope
Controlling object height above runway
Controlling object distance from runway end
Controlling object centerline offset.

It seems that it's an obstacle near the airport, but I can not tell why it is more important than the others. Does it lead to the most adverse situation, as far as aircraft's climb gradient is concerned? Does also the term "Controlling Obstacle" exist?
Could someone point me in the right direction?


text:
Reason for limited engine fuselage on Sukhoi fighter aircraft?
To my amateur eye, there appears to be limited fuselage on the engines for Sukhoi fighters from Su-27 on.  That is, the fuselage follows the curvature of the engines closely and there is a definite material difference between the adjacent fuselage.

This seems to be a characteristic specifically of Sukhoi fighters or their clones.
What is the purpose of such a feature?
I realise might be a state secret as to the actual design decision and will accept such an answer but I suspect there is a straight-forward engineering reason.  And perhaps I am mistaken on my assessment.

The metal finish in the afterburner region is simply because paint will not endure the peak temperatures there. If that does not answer the question it is because I have a hard time to understand what you want to ask.

@Dave appears to have understood my question.  Perhaps my vocabulary is wrong.  F-14 from the straight back view does appear to have a very similar appearance, was not aware.  The limited 'skin/fuselage' or the low cross-sectional area of the aircraft near the engine area is what I was curious about.  I guessed the paint difference was from the heat, but I reasoned that was decided because the skin is so close to the burner.

That is, why are they able to place the skin so close to the engines?  I was expecting something like: Sukhoi engines are generally simpler and they can get away with it, or it just performs better in wind tunnels, easier to get to in the field, or all!  Help clarify?

In a fighter you generally want to optimize fuel and ordinance capacity as well as have competitive performance. This use case generally leads to a design that is different than your average transport category aircraft. The SU-27 has some similar characteristics to the F-14 Tomcat and it should be noted

The aircraft had a large wing, clipped, with two separate podded
  engines and a twin tail. The ‘tunnel’ between the two engines, as on
  the F-14 Tomcat, acts both as an additional lifting surface and hides
  armament from radar.

Here is a good picture of the engines from the back

(source)
You can see that they could connect the engines but that would increase cross sectional area, disturb the center portion which helps add lift and add weight. If there is nothing they need to stick in there, there is no reason to have such an area on the aircraft. Its also worth noting this is not terribly different from the back of an F-14.
There is not necessarily a whole lot of metal surrounding any aircraft engine.
In the case of the SU-27 it also looks like the engine coverings are unpainted, this may be for heat related reasons.

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text:
Why was the production of the Lockheed SR-71 Blackbird halted?
Why was production of Lockheed's SR-71 Blackbird halted, given that it was an advanced supersonic jet that was ahead of its time?

Are you referencing the halt in physical production (that all occurred early on) or the full on retirement of the aircraft, it flew well into the 90's despite not having been produced in almost 3 decades.

Production stopped because the USAF had enough aircraft to carry out the duties it was required to fulfill - infact, the USAF ended up with enough aircraft for a couple to be permanently based with Lockheed for the duration of its operational life for continued test flights.  There was no need to build a massive fleet, because there was no operational requirement for a massive fleet - a massive fleet would also have meant a much larger support budget (more KC-135Q conversions to carry the SR-71s fuel for a start), which no one wanted on their political plate.

So far unmentioned satellite downside: Sophisticated enemies know when to expect the next satellite overflight and can plan accordingly.  So far unmentioned SR-71/U-2 downsides: The requirement for a pilot.  While vital in many circumstances, humans & their support equipment have high costs.  Downed UAVs don't give the enemy a human propaganda tool.

@JonStory Being fast in itself does not make it advanced. It lit up radar screens like a light house, leaked fuel on takeoff, had film cameras, and its aerodynamics are only marginal for it's speed. It all depends on your definition of "advanced"

Why did they stop building it?
Because they built 32, and that was as many as was needed at the time. 32 spy planes was plenty for the USAF/CIA to use, so building more would have been a waste. By the time those airframes may have needed to be replaced after 30 years or so, the SR-71 had been withdrawn from service and there was no need to build any more.
I think the question you're really trying to ask, though, is:
Why was it withdrawn from service?
And why wasn't it replaced when it was withdrawn?
The answer to those questions is a bit more complex, but essentially comes down to "Because it wasn't really needed any more."
The SR-71 was designed and built in the 50's and 60's. That means it was designed shortly before the first space flight, and built shortly afterward.
When designed, there was a huge need for a fast, "impossible to shoot down" reconnaissance aircraft. The SR-71 suited that - it could dodge missiles just by outrunning them, and by the time any adversary scrambled a fighter and got to the SR-71's altitude, the SR-71 would be a couple of hundred miles away and possibly even over a different country.
So what happened?
Satellites happened.
Why maintain a fleet of very high maintenance planes and keep them on high alert, then fly them over your rival's airspace? That's expensive, time consuming, difficult, risky, and (quite understandably) tends to upset your rival. It was, in short, an expensive way to annoy Russia and China. Okay sure, it got some reconnaissance too, and did its job (as an aircraft) beautifully, but when times are tense the last thing you need is to antagonise each other.
As an aircraft, then, it was a huge success... but as a geopolitical pawn, and as a military asset? It's a little more questionable. It certainly performed a vital role, but it had negative downsides from doing that.
Fast forward a few years, and we developed reconnaissance satellites with a whole bunch of advantages

With a few of them in the right orbit, you can have a satellite over an interesting part of the world pretty much 24/7. Even without that many, you can pass over an area pretty regularly.
Less obvious. Okay, your rival does not like you launching them - but once in space they're just "there", there's no antagonising "Oh look, an SR-71 flying over us"
They're "fire and forget" for the most part. Once in space, you just use it: you don't need to keep a bunch of pilots and aircraft on the ground ready to fly
It's less obvious what you're looking at, and when... if an SR-71 flies over the base that contains your new secret weapon, you're gonna notice. But when a satellite flies over for the 18th time today? Not so much
No planning and preparation time (which, for an SR-71, was a huge undertaking).  You just start taking pictures, or wait for a satellite to get to the right place, then start taking pictures.

They have disadvantages, too

For 24/7 coverage, you need quite a lot of them, and they aren't cheap
You have to replace them occasionally (and/or boost them into higher orbits)
If you upgrade your camera, it's a lot harder to replace the one on a satellite than an SR-71

But overall, a satellite is a more reliable, less antagonistic way to spy on your rivals. They're not perfect, but you know you've got permanent spying capability with no need to plan your reconnaissance ahead of time.
In short: It wasn't needed anymore.

Nice answer. One nit-pick: If you need to spy on a new location, it does take some planning to get a satellite over that new location, be it adjusting the location of a geosynchronous satellite, or an adjustment of a lower orbiting satellite, they just don't apparate to a new location. As I said, minor nit-pick.

True, I didn't want to get into too much detail of orbital mechanics though - that could fill pages on it's own. Typically you'd set up your satellites to have good coverage of your rival, particularly their interesting locations, and run a constellation of satellites rather than one or two. For simplicity's sake, I'll leave the answer for now and let your comment (and this one) do the explaining :)

Also worth noting that the U2, a sorta similar spy plane, had a shoot-down incident around this time as well. That put a lot of skepticism into the spy plane program.

There is one additional disadvantage of satellites vs. spy planes: The SR-71 flew at up to about 16 miles above the surface, usually somewhat less. Satellites will be hundreds to thousands or even tens of thousands of miles away from the surface. Also, the satellite will have to deal with more atmospheric distortion. Thus, satellite photography will usually be nowhere near the photo quality of aerial photography.

As another addendum to your answer, the Soviet Union developed technology such as the MiG-31 and the R-33 missile capable of shooting down an SR-71. Which, according to this article stopped any future overflights of Soviet territory.

Plus we have the Open Skies treaty, which means we can openly fly ordinary spy planes over Russia (and vice versa) without fear of them getting shot down.

@Random832 True, although the Open Skies Treaty is really more about monitoring than short term reconnaissance: you can't just waltz up and fly over whatever you want to see, so the observed country has time to just hide things it doesn't want to be seen

To add to this answer: I was wondering how good the digital images were compared to the analog ones in the SR-71. Apparently the satellites also used film, they flew only 150 km above the surface, and missions were usually only a couple of days. https://en.wikipedia.org/wiki/Corona_(satellite)

@Random832 Open Skies doesn't work like that. First, each country only has a limited number of flights per target country per year and that number is at most a few tens. Second, each country has the right to conduct the Open Skies flights over its own territory itself, which the USSR insisted on and, I believe, Russia maintains. So, what Open Skies actually means for spying on Russia is that, a few times a year, the US says "Fly one of your planes over this route at this time." and the Russians say "OK" and hand over the photographs of themselves that they took.

This answer, in no way, accounts for the fact that the U-2 is still in widespread use.  Clearly there is a place in the US surveillance inventory for planes flying around 70k ft, as we still have one.  The "it was replaced by satellites" argument is simply wrong.

@JayCarr there was no need for two... There's still a niche role for the U-2 which is also significantly less maintenance intensive.

@JonStory Maybe, though I'm yet to see anything more than conjecture on this point.  At any rate, the only point I'm making here is that the "it was replaced by satellites" argument is bunk (or, at best, just an opinion).

@JayCarr can you give an example of actual spy overflights that the U-2 would operate on instead of the SR-71 or military satellites? I know that NASA holds several U-2/TR-1 hand-me-downs from the CIA or Air Force, but these are only used for weather testing and technology demonstration; most radar technologies nowadays could easily detect a U-2 overflight at its ~70k cruise alt. What military purpose would the U-2 even have that you argue could compete both strategically and tactically with satellites?

Just a follow up to my previous comment: I suppose that (HIGHLY improved) side-looking radar would be a possible solution to its technological shortcomings but would that be enough for the Air Force to pass the operation by penny pinching generals? The whole concept of the U-2 still being a viable tool to ahem observe Russia or other major powers is a bit hard to swallow for me. Of course, that may be what they want us to think... ;)

For several reasons:
First off, the SR-71 was a plane which was never intended. An earlier Blackbird incarnation, the single seat A-12 had been in service for several years with the CIA under the codename Oxcart. When the veil of secrecy was lifted and the USAF discovered it, the Air Force demanded to be responsible for strategic aerial reconnaissance. Internal politics between the DoD and the Johnson administration facilitated this.
The Air Force expressed interest in the Blackbird for two missions: first, as a long range interceptor and fighter escort for the B-70 bomber project in parallel development at the time and as a high speed reconnaissance aircraft with expanded surveillance and electronic countermeasures onboard. Both roles would require a two person crew in order to operate the systems, leading to a longer aircraft with a second crew station.
The interceptor version of the Blackbird resulted in the YF-12A prototype first flown in 1963. It featured a two person crew as well as cropped nose chines and a conical nose radome for the AN/ASG-18 fire control radar and the recognizance bays were refitted as weapons bays to carry the AIM-4 Falcon air to air missile. The program was cancelled in favor of the XF-108 Rapier aircraft, itself cancelled along with the XB-70.
While the A-12 finished off its service life and was quietly retired to Palmdale and Area 51, the SR-71 would have an outrageously successful career with the USAF despite mixed feelings with the program amongst the top brass. Gen LeMay hated the Blackbird and felt the Air Force should spend its program dollars on bombers, not on a high maintenance speed demon for reconnaissance.
The SR-71 program officially retired in the late 1990s but all throughout its career, Lockheed attempted to sell derivatives of the aircraft for various defense programs. Lockheed submitted Blackbird derivative designs for the F-X fighter program, which became the F-15. And early incarnations of Lockheed's proposal for the Advanced Tactical Fighter, which became the F-22, were based upon the Blackbird.

LeMay could hate as much as he wanted: the SR-71 first flew in December 1964 and LeMay retired in February 1965. And, while we're at it, [citation needed] for the claim that LeMay did hate the SR-71. Neither the Wikipedia page for the General nor the plane mentions him holding any opinion about the plane, except for being very sure that it should be SR-71 and not RS-71. (Obviously, something not being mentioned on Wikipedia isn't evidence that it's false but you'd expect something that important to be there.)

@DavidRicherby I'm not the OP so can't point you at their sources for "Hated", but here's some context on LeMay's position on the SR-71. I don't believe he hated the SR-71: rather that he had other projects he preferred (primarily the B-70) https://goo.gl/ua8oj9

@JonStory Thanks -- that interpretation seems more plausible, to me.

Production of the SR-71 halted, quite simply, because they had built as many of them as they needed (or, perhaps, as many as they could afford). Pretty much like everything else, really.

The SR-71 was a special plane with capabilities beyond what are commonly known.  It was also incredibly expensive and was limited by high maintenance costs and special equipment requirements which were housed at only limited facilities.  If for instance a blackbird was forced to land at a facility other than one of those handful of authorized and certain equipment was not available to service that plane before it cooled down, it would be required to do a few million dollars in repairs and the plane would be grounded until that work was completed.
At the time of construction, the number of planes needed, plus a few spares were built.  No additional units were ever ordered because the equipment to make them and their parts was also very expensive.  As no other crafts shared those parts, such as the engines, there was no economical justification for keeping that equipment either, so by the 1970's most of that was dismantled and without enormous expense, no more could be made.  Parts were exchanged between planes, sometimes, to keep the fleet operational well beyond its expected life cycle.  Because of part deformations through the extreme flight conditions encountered, exchange was not always possible, so sometimes when something like a bolt wore out, a replacement would need to be fabricated because the stock threading no longer even fit, so a bolt might cost many thousands of dollars to replace.
Even with these constraints, the ability to quickly respond to the need for threats meant the SR-71 was kept in service well beyond intended or economical life cycle, until obviously other platforms became available and relieved the need.  Those platforms are simply better or a way would have been found to keep the beast in the air.  Nostalgia or just pure love for a great design was not enough to justify keeping it active.

According to Wikipedia, Lockheed was ordered to destroy the production tooling in Febuary 1968. So, yes, by the 1970s, that should all have been gone. Also, this answer mostly deals with why they couldn't restart production after they stopped, and why they finally stopped using the plane, rather than why construction was halted.

Having worked on components of the SR-71 and with the pilots, I can assure you their are many things in Wiki's and articles about the plane that are not exactly 100% truthful such as what is really the top speed of the plane, but yes, tooling began being dismantled in the late 60's.  The big hit was the last engines were build in the 70's and then that equipment was salvaged.  In the end, no more were built because other platforms were developed and planned with the intent of covering the need and the ability to build more was intentionally removed to prevent asking for more.

I'd appreciate some examples on what "million dollars in repairs" would be needed if the airplane wasn't serviced properly immediately after landing.  Examples of the high maintenance costs and part deformations would be nice too, if only because I'm curious.

The operational extremes of the SR-71 were such that components would heat during flight and deform.  When they cooled, the parts would be not only temper, they would not return to original specifications.  External components typically could not be moved between units.  Threading on screws for example would not longer be to original specs so had to be marked during repairs to make sure they were re-assembled in the correct location for proper fit.

Lubricants used in the Blackbird were solid at normal air temperatures.  When the plane landed, special equipment had to be available to get it out and into storage before it cooled, and preheat it for re-insertion before flight.  If that equipment was not available, the lubricants would solidify and the assembly had to be taken apart and cleaned by hand, then reassembled an expensive and lengthy process with the plane off line until it was complete, relocated to an authorized facility, and declared flight worthy.  There were few such facilities, all were originally part of SAC I believe.

Also, camera and lens technology and communications tech advanced to the point that a fast-moving plane just couldn't match.
The SR-71 was an angel in the air and a devil on the ground. It took a lot to keep the people safe both on the ground and in the air.

I don't understand. The SR-71 was a plane that was built solely to carry cameras. The SR-71 wasn't a competitor to cameras: it was a device for putting cameras in the air above things that the US wanted to photograph. Better cameras would make the SR-71 better, not make it redundant.

Actually, I was wrong to say that the SR-71 was "built solely to carry cameras." It also carried other things. But carrying cameras was a huge part of its mission.

authors: امیرحسین خدائی

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


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Where can I find reliable data on maximum turn rates for jet fighters?
I'm looking for reliable data on maximum instantaneous turn rates for jet fighters, something coming from reliable sources, ideally official flight manuals or specifications. I can't seem to find anything. I've seen reports of turn rates around 35°/s for some fighters (F-22, Typhoon, Rafale) but I don't know whether those can be trusted: https://defenseissues.wordpress.com/2014/01/11/comparing-modern-western-fighters/
If possible I'd like to have data on fighters with exceptionally high maximum turn rates, but really, anything would be welcome. Even information on old, retired fighters would be nice, and I guess that's more likely to be declassified. Failing that, a lower bound would be useful.
I don't know if turn rates make much sense for helicopters, but that information would also have some value.

I'm going to assume that most of that information is classified.  Most governments go to great length to cover up the performance characteristics of their jets.  You may be able to find some unclassified numbers if you dig around a bit, but I would suppose they would be well short of actual capability.  Janes may be a good resource for this: http://www.janes.com

Imformation on the F-22, particularly performance and mission systems data remains classified, as with the F-35 airplane.  To the best of my knowledge there isn't much technical data available to the public on those subjects.
Now flight manuals for older fighter aircraft are readily available to the general public.  PublicIntelligence.net is a great source for these documents, as they have them for the F-14, F-16, F/A-18E/F, AV-8B, A-10, just to name a few.
Janes/IHS is not a great source for this stuff; their entries are more on the level of intelligence briefs and encyclopedia entries and are not likely to contain the information you ar looking for.

Thanks, I'll dig around and see if I can find something on PublicIntelligence.net!

While it's an interesting question, the actual answers are not very meaningful.  Max instantaneous turn rate is a corner condition where you will give up all your energy leaving you very vulnerable. The key to fighter maneuverability is energy management.
A good discussion on fighter maneuverability is available at this link.
Additionally, I would suggest researching Col, John Boyd, USAF.  He did much of the early research in energy management.

The mention of Boyd is very worthwhile, he came up with the idea of specific excess performance as a meaningful way of comparing fighter aircraft manoeuvrability and his biography is a fascinating, very well written book. SEP charts are a much better way of comparing manoeuvrability, as they show the advantage / disadvantage across the whole flight envelope, where as instantaneous turn rates can be chosen at a point in the sky (speed/altitude) that makes the given aircraft look favourable.

You need to look up Flight Data on the F-16. It was designed to be an Agile Fighter aircraft using specific formulas for aircraft energy Calculations. The flight data is also NOT Classified: NASA is a public organization and required to disclose it's information, and ran a series of High Performance tests with an F-16 and through a Wind Tunnel that are publicly available (but that I don't have a link to at the moment.


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Why is there a white line on Russian fighter jets' instrument panel?
In several Russian fighter jets (e.g., MiG-29, Su-27) there is a white line on the stick that matches with another one on the instrument panel. Is there any reason for this?

Cockpit of a mig29

Cockpit of a Su27
A former flight instructor told me that it was to help pilots recover from a spin: when the two lines match, the stick is in the proper position to stop the spin. Is it true or is there any other reason?

The white line is painted on the instrument panel.  The canopy is the curved, clear cover.  I've taken the liberty of editing the question to use the correct terminology.  Great question, by the way.

@WayneConrad I was staring at the canopy for a long time and I couldn't see a line. =D

me too...   lol  :)

You were right, sorry about that

I believe it is exactly what your instructor has said - it helps when regaining control of the aircraft during a spin.
The correct procedure for recovering from such a maneuver is to apply rudder in the opposite direction. Then, keeping the control column centered, move it forward (for an upright spin) or backward (for an inverted spin).
The problem is, when you're in a spinning aircraft everything outside is a blur and the G-forces involved can throw off the pilot's perception - this is of course especially true of inexperienced pilots. The white line painted on the control column in your picture was one method for helping the pilot to keep the stick centered. Having something simple to concentrate on helps immensely, and is more intuitive than looking at the yaw indicator.
Source: Flying at the Edge: 20 Years of Front-Line and Display Flying in the Cold War Era,
by Tony Doyle.
Edit: This book is an autobiography of a Cold War era RAF pilot, and while it does directly mention the white line painted in the cockpit, it does so in reference to Vampire and Meteor aircraft. I cannot find any reference specifically to Russian aircraft anywhere in the book, and neither does there appear to be any picture evidence of the stripe in the cockpit of any British aircraft. Perhaps someone else can source more evidence.

Confirmed here in the photo legend.

I saw a defected Chinese MiG-15 around 1963. It had a flat black interior with black instrument dials with white legends and pointers. There was a 5 cm white stripe down the center of the instrument panel, and the control stick was also white. I assumed that the pilots were instructed to "put the white stick on the white stripe" to recover from a spin.

The white line is indeed for spin recovery, the Mig 15 procedure is to put the stick against it, count 3 revolutions, if the aircraft is not recovering then eject !


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What is "clearance delivery" meant for?
I was recently having a conversation where the term "clearance delivery" popped up, and was talking about his time flying into PHX, but in all of my time flying, I've never heard of the term before! Could someone explain to me what exactly is this for, and where would you find this?

"Clearance Delivery" is exactly what you've surmised it is - a frequency used on the ground to copy your initial clearance from ATC before you take off.
The idea behind using a dedicated frequency for this is that it avoids tying up the ground control frequency (used for authorizing ground movement on taxiways and such) with long clearances and readbacks.
Clearance Delivery is found at controlled fields. Pilots operating under Instrument Flight Rules will generally use it prior to each flight, and at airfields in class C or class B airspace it's used by VFR pilots as well (since they'll be talking to departure controllers very shortly after take off until clear of the controlled airspace).
At less busy fields Clearance Delivery is often staffed by the same controller working Ground (e.g. at Long Island / Mac Arthur it's usually the same controller working both positions), and at some airports clearances will be read over the ground control frequency when it's not busy. At busier airports clearance is usually its own position - possibly with multiple frequencies (e.g. at La Guardia there is a separate clearance frequency for helicopters).

At less busy controlled airports, there very often isn't a clearance delivery frequency at all.  Only the ground frequency even exists.

@Lnafziger Yup. And at some fields that have both they'll tell you to call on ground instead if it's one person on both positions and they don't feel like dealing with two frequencies.

Yup.  Usually in this case, it will say on the ATIS that "clearance delivery and ground control frequencies are combined on xxx.xx".  I love the people that call on clearance anyway.  Ummm...  didn't you listen to the ATIS??

Take a look at http://www.ourairports.com/airports/RJAA/pilot-info.html. I got it from Google checking to see if Narita still had not only a Clear Delivery and ground frequency, but also (at least as I remember it) an engine start frequency. I don't see that there specifically, but they have a separate ramp frequency in addition to clearance delivery and ground frequencies.

At even less busy airports, there isn't even a ground frequency and tower handles everything (EDFM is one example)

Some airports also use clearance delivery for ground metering.  At KEWR in particular once you are at the edge of the movement area you call CD and then monitor ground for taxi.  This is to prevent the clutter of initial calls on ground as that position can get easily saturated during departure blocks.

Some non-towered fields have a remote Clearance Delivery RCO, and the remainder now have a phone number to the overlying ATC for the same purpose.

Also, CD can usually be used to pick up Flight Following.

@ randomhead I had to rollback your edit because it dramatically changed this answer (see How much should be added to an answer by another user? on Meta). Please submit your text as a new answer.

@Bianfable obviously don't want to get into an edit war, will bring up on Meta when I have a chance, but I think there's a difference between my edits and expanding an answer from one sentence to four paragraphs...

"Clearance Delivery is found at controlled fields"-- "controlled" = "any field in controlled airspace" -- or -- ??  (That's definitely what the phrase used, to mean-- but maybe someone changed it lately?). ??


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What is this instrument that has "PACK" written on it and a temperature scale?
All I know right now is that it’s made in 1973. Another instrument I have is from a b727 and is dated 1982. This one I have no clue. Serial number- H 2590. The brand is Amphenol. That’s all the info I can find. I have some pictures.

It looks like the pack temperature gauge for the air conditioning system on the 727

To monitor the operation of the air cycle machines, each has a
  temperature transmitter at the outlet off  its compressor.  The
  temperature sensed is displayed on a pack temperature gauge for each
  pack.  As more air is directed through cycle machine to provide more
  cooling, more compression is  required from the compressor.  This
  results in a higher compressor outlet temperature.  Therefore, the
  pack temperature gauge monitors air cycle machine work load.  To
  protect the compressor from excessively high temperature an over
  temperature sensor at the outlet of the compressor will cause the pack
  to shut down if the temperature reaches the limiting value.  Another
  temperature limiting sensor located at the inlet to the turbine.

You can find a full video of how that section of the flight engineer panel works here.

Here it is on the flight engineer's panel (airliners.net).


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What does pneumatic operated and electrically controlled means?
I was going through A 320 FCOM and didn't understand this term

Pneumatic operated: actuation by using air pressure. By opening a valve, high pressure air enters a cylinder, causing a piston to be pushed out. Typically, actuators of this type have two valves connected to two separate chambers, allowing for movement both ways.
The valves need opening and closing, though. This is what the "electrically controlled" part means: a small electric (typically electromagnetic) actuator will open or close based on an electric control signal.


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What is pendulous suspension in magnetic compass?
I am not able to understand what is pendulous suspension and how centre of gravity and centre of suspension are related in magnets and their errors. Can someone explain this in layman language or could share the link which gives good 3d animation of the same.

Research the "Bohli" compass and understand why it is free of turning errors--

This video covers it pretty simply.  The compass magnets are attached to the bottom of an upside down cone, which is resting on a spike.  The weight of the compass magnets, and the center of gravity of the assembly as a result, is near the bottom of the cone and the "hang point" is up near the top at the tip of the spike.
It's a cone pendulum; basically a lady in a hoop skirt, out on the dance floor (put a couple of bar magnets alongside at at the bottom of the skirt, stick her in a vat of kerosene to dampen the skirt's movements, and there's your compass-lady).
The pendulum arrangement keeps the compass magnets more or less level to the earth even if the spike it's on is tilted (mostly to accommodate changes in pitch attitude with speed and stabilized climbs and descents), within the range of movement of the cone.  Compass units in ships (and very early aircraft compasses) achieve this by having the compass float on water (or some other fluid) within the housing so the compass can stay horizontal while the ship pitches and rolls.
The various turning errors relate to how the pendulum reacts to accelerations and apparent gravity (think of the lady's hoop skirt tilting off vertical as she starts to move, for example), the C of G of the cone being below the hang point, while at the same time having the magnetic alignment forces acting on the magnets. The result is readings that wander in specific directions (acceleration/deceleration and turning errors) if there are any lateral accelerations going on, and while the magnets are rotating, because of the "struggle" going on between the magnetic forces and the inertial forces.  The compass reading is only valid when the inertial forces have gone away, when there is a steady state condition of no turns and constant speed.

Thank You John !

John the video was very nice and your explanation was superb. But in the video they mention that in compass digits are in reverse order I am not able to understand that.

It's because you are looking at the lady from behind outside the skirt, and she isn't turning but just stays aligned with north, while you are moving around her from the outside.  The N is printed at the BACK of her skirt and you see it when south of her.  If you move around so you're facing west, you're moving around to the EAST side of her, and that's where the W on her skirt is, to tell you you're facing west. Put numbers between N and W and it counts down from 360 at N to 270 at W.  You are turning to the left, but the progression of the numbers IN YOUR VIEW is to the right as a result.

Hi John. You have explained and shared me good content. I am facing a lot of difficulty in understanding gyros and gimbals and their working, axis of freedom etc. Do you you have a video link for that...

Just go on youtube and search "aircraft gyro" and it'll present a number of videos.

Thank you John


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What is a bowed rotor?
I was going through A320 FCOM and came across this term. Is bowed rotor bending if the spool due to unequal thermal cooling

Maybe if we had some context...?

I believe he may read it from here https://aviation.stackexchange.com/q/84444/679


text:
Why was blue hydraulic system chosen for RAT?
Q1. Why is blue hydraulic system chosen for RAT out of the three.
Q2. If in case of hydraulic emmergency if I push RAT switch on Emer Elec pannel what will happen

Because in A320 is the only hydraulic system independent from the engines and isolated from the other two hydraulic systems (while G and Y have the PTU in common). Also the B hydraulic system is able to control both elevators and ailerons, while Y cannot control ailerons and G controls only the left elevator. That's a design choice taking in account all the possible failures to reduce the risk of a triple hydraulic failure.

There are two switches that allow you to open the RAT:

The RAT MAN ON (on HYD panel), which open the RAT and feeds the B HYD
The RAT MAN ON (on EMER ELEC panel), which has the same effect of the previous one, but it also connects the emergency electrical generator

Please also note that in case of a dual engine loss, the RAT is automatically deployed.

I read somewhere that in case of electrical failure the electrical motor of blue hydraulic system stops so blue hydraulic failure occurs

Yes, and this is why you deploy the RAT in case of a dual engine failure, because you have no electrical power to run the B or Y elec pumps. As you can see in the diagram above, the RAT is alternative to the elec pump, so it can pressurize the B hyd system without the need of electrical power


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What radio equipment do pilots use to communicate with ATC?
I know of the transponders used for communication by Air Traffic Control, but apart from that, what radio equipment do pilots use to talk to ATC? What modulation method is used?

Welcome to aviation.SE! This seems like quite a broad question, you might like to read through some of our existing radio questions and see if you can be more specific. For information on frequencies, see this question.

Also related, maybe even a dupe?

https://en.wikipedia.org/wiki/Airband
emphasis added

As of 2012, most countries divide the upper 19 MHz into 760 channels for amplitude modulation voice transmissions, on frequencies from 118–136.975 MHz, in steps of 25 kHz.

A typical plane often has two communication radios, referred to as COM1 and COM2.
Each radio has an active and standby frequency. The pilot can listen to either radio, or both radios at the same time, but can only broadcast on a single radio.
There are often 2 navigation radios as well, NAV1 and NAV2, which can be tuned to VORs or other radio beacons, and the pilot can listen on those radios (typically for Morse Code IDs, Recorded Voice broadcasts, and occasionally, Voice-over-VOR ATC)

Here's a neat info graphic to help visualize the frequency distribution

The major communication tools are obviously Vhf radios for voice, another one is HF, particularly in remote place or oceanic. In tran atlantic the voice comms are thru HF with SELCAL( selective call) which brings another communication tool more and more used : CPDLC( controller pilot datalink communications) this one is not by voice. Clearances or requests are given by this method certainly for transatlantic and more and more in land as well.

A short summary, specific to the US:
VHF AM is the most common voice mode for communications with ATC.
UHF AM is also used for military and some government services, but generally just military, for communication with ATC.
HF radio is used for communications with ATC, and is most often used on oceanic routes.  It is not as "reliable" as VHF, but the signals will propagate farther.
Other enhancements and other modalities are available but they are not strictly voice communications.
14 CFR 87 covers aviation services, and defines frequencies and modes as well as uses for aviation specific services.
https://www.law.cornell.edu/cfr/text/47/part-87

This is a very broad question just because every type of aircraft has different requirements for its design purpose. As civil aircraft may not need to use UHF frequencies where some military aircraft must have an UHF radio.
And transponders are not used for communication. :)

Transponders ARE used for communication:  When you press IDENT and the controller responds, that is communication. When you change your squawk code or Transponder mode, and the controller sees it, that is communication.  Not all communication is Voice.

Hmm, you are right. But as far as I understand, @joey asks about radio telecommunication. I mean two-way-communication. Not identification or telling ATC that you are in Emergency over transponder not over radio.

ICAO Doc 8168 Vol 1, page 245 and others depicts how transponders will be used in case of COMMUNICATION FAILURE. I am still looking for other documents supporting that transponder is not a Communication device. Its used for Identification. [link] (http://www.chcheli.com/sites/default/files/icao_doc_8168_vol_1.pdf)

FAA Handbook. Page 55. (https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_Ch11.pdf) “verbal communication” and transponders. I got a -1 , no problem.  :) I am still looking for  Documents. And will wait an answer from @joey.

(whispering) I am not arguing with myself. This helps me read more. That’s all. :)


text:
Why are the modulation depths of the localiser and glideslope different?
Why do we use a modulation depth of 20% (for 90Hz and 150Hz each) in the case of the localiser and 40% (for 90Hz and 150Hz each) in the case of the glideslope? Why not use 20% for both?

Where did you find the 20% and 40% numbers?

Crossroads its v.basic thing that u are asking however for your reference see the link below

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.indracompany.com/sites/default/files/normarc_data_sheets.pdf&ved=2ahUKEwi6k9Lz9b7aAhUHkCwKHQMLAukQFjAEegQIABAB&usg=AOvVaw2afYc410PsVA9qPlo9QkMS

From the book "Principles of Avionics" By Albert Helfrick:

The amount of modulation is twice that found in the localizer. Because the glide slope does not have ident or speech audio, the percentage modulation for 90 and 150 Hz tones is increased.

Fiddlesticks i would humbly disagree to this !!! I dnt think this is the reason. Mod depth is doubled in glideslope's case than localiser and also note down glide slope is using UHF band not VHF unlike localiser. There must be some other reason. Cole on folks come up with proper reason m dying to hear :(

@aadeez "Mod depth is doubled in glideslope's case..". Yes, that is precisely what the book I linked to says! (Click on the link if you haven't already).

@Rumi, you mean pages 88 to 93? That explains, in somewhat complicated way, how a directional signal is transmitted using two or several simple dipole antennas and suitable phase shifts. I think the Wikipedia article on Phased Array does better job of explaining the general principle.

In short
In addition of the two navigation tones 90 and 150 Hz, the LLZ signal can contain two other components:

a telegraphic identification tone of 1020 Hz,
a voice channel, between 1 kHz and 3 kHz (3dB). This channel can be used by ATCO to talk to aircraft crews when their regular communication receiver has failed.

All components have a modulation depth specified by ICAO. The total depth is the sum of the individual depths.
There is no need to duplicate the identification and voice elements on the UHF carrier, the GP signal carries only the navigation tones.
To have LLZ and GP carriers modulated with a similar (total) depth, the individual depth allocated to the two navigation tones is smaller for the LLZ than for the GP.
The resulting total depth is between 68% and 95% for the LLZ, and between 75% and 85% for the GP.
If you are interested, relatively complex details follow.

Modulation index for a compound signal
What ICAO calls the depth of modulation is better known as the modulation index, this is the wording I use here. In DSB-AM the index is the ratio of the total amplitude of the modulation to the carrier amplitude.
Strictly speaking, the total amplitude of the modulation is itself the sum of the phasors of individual modulations. Since the allowed zero-crossing phase difference for tones is only 10° or 20° and there are restrictions for other elements, phasors are nearly aligned. In such a case the total peak amplitude can be approximated by the sum of individual peak magnitudes, and the total index can be approximated by the sum of individual indexes. Let's use this approximation and work with indexes only.
Total indexes for LLZ and GP
For the LLZ, with identification keying and voice capability:

The minimum index is 68%: 18% for each navigation tone, 5% for the identification, and a voice channel 9 times the identification tone (45%).

The maximum index is 109%: 22% for each navigation tone, 15% for the identification and 50% for the voice channel. But this would over-modulate the carrier, which is not desirable as this increases the VHF channel spacing and prevents simple demodulation by envelope detection. ICAO limits the total index to 95%.

On the other hand the GP signal contains only the two navigation tones which individually modulate the UHF carrier with an index between 37.5% and 42.5 %, this means the GP carrier is modulated between 75% and 85%.
Both the LLZ and the GP carriers are modulated with about the same total index. The part allocated to the two navigation tones must be different for LLZ and GP to get this result.
Of course, without a voice capability, the LLZ index is lower, between 41% and 59%, hence the navigation tones index could be increased in this case. However the receiver expects fixed indexes.
The two next sections summarizes Annex 10 specifications for reference.
LLZ specifications

§3.1.3.5.1: 90/150 Hz nominal index of 20%.
§3.1.3.5.2: Tolerance: 18% to 22%.
§3.1.3.5.3.3: The two tones are phased-locked.
§3.1.3.8.3.2: Voice index 50%, ratio 9:1.
§3.1.3.9.2: 1020 Hz tone index between 5% and 15%.
§3.1.3.8.3.2: Total index limited to 95%

The annex also provides a limit on the sum 90 Hz + 150 Hz:

§3.1.3.5.3.6: Between 30% and 60% (after January 2000).

This is related to how the LLZ signal is created. While it appears to be a single signal to the receiver, it is actually the space modulation result of three physical signals sent on the same frequency by the antenna array:

The Carrier with Sidebands (CSB), a DSB-AM signal sent along the course axis with no phase shift.

The Sidebands Only (SBO), a carrier-suppressed AM signal, sent on one side of the course axis with a +90° phase shift, and with a -90° phase shift on the other side.

CSB and SBO are modulated by the two navigation tones with the same index. The DDM is created by the space modulation after they are radiated. Navigation tones from CSB and SBO add on one side of the course axis, and subtract on the other side, in different a proportion according to the azimuth. For details on the ILS principle, see this question or have a look at this video.
GP specifications

§3.1.5.5.1: 90/150 Hz nominal index of 40%, tolerance: 37.5% to 42.5%.
§3.1.5.5.3: The two tones are phased-locked.

Ok folks in my view the reason of using different mod depths for localiser and glideslope is this : As we all know that increasing the mod depth, increases the Total power or Peak Envelope Power of the signal. Now Glideslope uses UHF band and for 90Hz and 150Hz it needs increased mod depth to be demodulated by the ils receiver in aircraft, whereas localiser uses VHF band hence less mod depth of only 20% is needed for each tone of 90Hz and 150Hz in this case. I hope you all will now excuse of all the brain storming that you have done so far. CrossRoads my friend was it me?

Disagreed. I dnt think its the case, the DVOR also is in VHF band with extremely low mod depth. Why the 40% mod depth was chosen for GP is still a mystery.

Appendix B of this document  https://www.faa.gov/documentlibrary/media/order/6750.24e.pdf
appears to refer to ICAO Annex 10,  http://cockpitdata.com/Software/ICAO%20Annex%2010%20Volume%201  .
See 3.1.3.5.3.3 and 3.1.5.3.3.4 for the Localizer, and 3.1.5.5.3 for the Glideslope.  That's why they use what is used currently; the International Standard says to.
As to the why of the particular modulations, I don't have the history of how the particulars were developed over time.  A google search of "ils approach history" yields quite a few hits tho.
This one seems quite detailed.
http://instrument.landingsystem.com/

Crossroads my friend the query of mine is still unanswered !!! There must have been a reason to use mod depth of 20% and 40% . Nothing in aviation is without logic. Someone can easily question why in localiser they didnot use 40% mod depth of 90hz and 150hz each? So my question still remains unanswered sadly which is quite disappointing to see :(

You need to go back to the 1940s for that I fear:  http://ethw.org/First-Hand:Development_of_the_Instrument_Landing_System_Glide_Path I'm still reading.

From Pages 5-2 and 5-4 here,  https://www.casa.gov.au/sites/g/files/net351/f/_assets/main/pilots/download/ils.pdf The localizer beam is centerline +/- 2.5 degrees, while the glide slope beam is centerline +/- 0.5 degrees. Perhaps that is why the modulation is different. But I haven't seen any words that say  modulation degrees corresponds to transmitted beam width.

CrossRoads i am still waiting for your indepth explanation my friend :)

Sorry, I haven't seen anything more as to how they came up with the depths used.

Who downvoted me on something from 5 months ago?


text:
What is a hypernym for the ascending and descending legs of a flight?
If an airline flight is everything that happens in between your starting and ending gates. What is the generic term for each time the plane ascends or descends during an air route? In layman terms, what terminology would define the four '_____?' equally as four separate things.

If the image below indicates the proper terminology for a flight. What is the hypernym for phase 3/4 and phase 6/7 of the air route?

The act of going up and down is called a "cycle". In aviation there is no word to describe both the climb/descent sections as far as I'm aware. I guess you could call it a half-cycle...

I would say the hypernym is "transition." You transition from climb to cruise and from cruise to descend. And transition, which is a term used in aviation discussions, fits nicely. To transition from cruise to descend you have to reduce power, retrim the aircraft, and do a number of other things depending on the particular plane. This "transition" from cruise to descent even has it's own check list as does the transition from climb to cruise.


text:
Why did the design of the Boeing 247's cockpit windows change for some models?
Have a look at this article on a famed example of the 247.
The image at the top is the aircraft during its flights with the RAF, likely some time in 1944. Note the reverse-slope windows that are a hallmark of the 247.
Now look at the other aircraft in the same article. They have conventional style slope-down windows. Those two images are from before 1944, one in the 30s and the second around 41/42.
Does anyone know what's going on here? Were certain batches one way or the other?

I'm certain that something like this has been asked before, well, more about why the reverse-slope was done in the first place.

@quietflyer This one? Not sure it's an exact dupe because this question seems to be about differences within one specific aircraft model.

Well, the (model specific) answer below looks to be straight out of the answer to that one. VTC as a dupe.

@quietflyer Ironically, it even has been asked by the same person. And the answer there says what happened: from the 247D on the window was sloped aft

"By the introduction of the 247D" - This is a question about a D model.

From the Boeing 247 article (emphasis mine):

The cockpit windshield of the first 247s was angled forward, instead of the conventional aft sweep. This was the design solution (similar to that adopted by other contemporary aircraft that used a forward-raked windscreen) to the problem of lighted control panel instruments reflecting off the windshield at night, but it turned out that the forward-sloping windshield would reflect ground lights instead, especially during landings and it also increased drag slightly.[13][14] By the introduction of the 247D, the windshield was sloped aft in the usual way, and the night-glare problem was resolved by installing an extension (the glarescreen) over the control panel.[15]

But this aircraft IS a D model... the mystery deepens.


text:
Where can I find data on past forecasts of planned aircraft production?
Does anyone know of a database which would list the expected production rates for various aircraft, at the time those aircraft started production?
Finding actual production to date is easy, but I would be interested in what was the original planned production. I am not interested in current forecasts, I am interested in past forecasts that have been made before or at the start of production for the particular aircraft.
E.g. Cessna 152 was assumed by the manufacturer to be sold at the volume of XX aircraft per year, when the production plan was put into place.

I don't know of any consolidated database listing the forecast of deliveries and future of the market, but usually aircraft manufactures lists their forecasts in documents available for the public like Airbus for the next 20 years or Boeing . This is a start.

Yes both Airbus and Boeing deliver 20-year forecast for the complete market. For Airbus there is a spreadsheet which may function as your database.
IATA also publishes 20 year travel forecasts, here is the latest. Airline travel is going to double over the next 20 years.
At he time of first production, forecasts for the aircraft are made based on market forecasts, plus the expected market share that the aircraft may achieve. Information that is of interest to the stakeholders of the company.

Right, I think I haven't made my question clear. I am not really interested in forecast at this moment in time, I am interested in forecasts for existing aircraft that have been done at the start of their production. The ultimate goal would be to make comparisons between the expectations vs reality retrospectively.


text:
Where can I find data on the number of single propeller aircraft currently in operation in the EU and US?
Are there publicly available data for aircraft registered in operation?
Specifically I am looking for number of single propeller aircraft in US/EU, ideally with aircraft types as well. However, any useful data of this sort would be appreciated.

You can download the entire FAA aircraft registration database and analyze it however you want.
I have no idea about EASA, but because aircraft registration is delegated to member states you'll probably have to look at each one individually (e.g. the UK). I don't know if all EASA countries consider aircraft registration information to be public or not.
You could also look for a commercial data provider that sells the data you need, of course.


text:
At KOAK, how can I get a passenger from the GA terminal to the commercial terminal?
I want to land at the GA side of Oakland International (KOAK) in order to drop my passenger off for a commercial flight from the main terminal. I was told by a local guy that they do not allow a taxi on B over to the main terminal so I would need to park on the GA side and grab a shuttle/crew car/Uber over to the main terminal. I've contacted two FBO's and they tell me of about $50 in fees just to stop in. Has anyone done this and what is the best way?

This is a specific question but I think my advice applies to most FBOs.
I fly out of OAK and your best bet is to try signature. Buy some fuel, ask nicely and if they aren't too busy they might be able to accommodate you.
They have given me rides on the ramp before when my usual gate was closed due to a power outage.
If not, then call a rideshare/cab

I got a hold of two FBO's on the field.  Evidently they were trying to negotiate with the port authority regarding fees for small single engine aircraft to no avail.  Landing fees are currently $49 and can not be waived with fuel purchase.  The FBO's also charge a parking fee and a handling fee which are significant but can be waived or reduced with fuel purchase.


text:
Why are the brake temperatures so high during the cruise?
While monitoring the A320 aircraft systems during cruise I noticed that brake temperatures are relatively high compared to the OAT. I have seen brake temperature indications range between 20°C and 120°C during the cruise, when the OAT is generally around -55°C.
I would have always assumed that the brake temperatures would naturally cool down, but even hours into a flight brake temperatures are consistently high compared to OAT. Is there any reason for this? I haven't been able to find any answer on the FCOM or FCTM.

See also: https://aviation.stackexchange.com/a/33028/3159

The brakes will be above ambient temperature of the departure airport due to the braking action during taxing.
While airborn there is little airflow to cool down the brakes, so this temperature will only drop of slowly. Plus the wheel-´well houses many different systems (hydraulics, also the packs are close by) adding heat and thus slowing and even stopping the cooling.


text:
Why are liquid ring compressors not used in a jet engine?
A question has been asked here before whether sliding vane compressors could be used in place of axial compressors on jet engines since they have a high compression ratio per stage (Why were rotary vane compressors never used in jet engines?), the answer being that the sliding seal would give out at the RPMs required.
What about a liquid ring pump?
It's essentially a sliding vane compressor where the seal is provided by the mass of liquid moving along the circumference. Is it possible to maintain a mass flow of the same order as axial compressors with these? Please ignore the question of cooling of the liquid for the purpose of this discussion.

Liquid ring pumps are usually used for creating vacuum, which has large pressure ratio, but low absolute pressures. They less suitable for high pressures, because high pressure deforms the liquid ring more.

Also note that for a jet engine (rather than shaft engine with Brayton cycle) mass flow is much more important than compression ratio. And number of stages is not relevant, the total weight is.

You said to ignore the cooling of the liquid, but that's something that cannot be ignored.  With the compression ratios achieved in typical jet engine compressors, the air leaving the last stage of the compressor may be 800 - 1000 deg F.  You won't find a lot of liquids that won't just completely vaporize at those temperatures.  Yes you could potentially cool the liquid, but the cooling apparatus would add a huge amount of weight, as well as consume a lot of power.

There are ionic liquids with boiling points around 450°C and minimal vapour pressures.

@FrancisL.: Which is still well below some of the temperatures he's talking about.

It's not just cooling. It would either add a lot of weight, as the liquid carried out with the flow would have to be replaced, or a lot of complexity in separating it.


text:
How does an inoperative Anti-Skid affect V speeds?
I am trying to figure out why is it that when you have an inoperative anti-skid system, the calculated V Speeds are lower?
I'm trying to see this from a performance perspective, could this be due to the brake energy limitation of the aircraft?

When you say it affects V speeds, I assume you mean V1 (and possibly VR), but not V2. V1 is usually calculated from the balanced field length, which is where accelerate-stop-distance and accelerate-go-distance are the equal:

(image source: boldmethod > Engine Failure On Takeoff: Do You Stop Or Go?)
While the accelerate-go-distance will be unaffected, the accelerate-stop-distance is affected by anti-skid because you will not be able to brake as efficiently as with anti-skid operating normally:

the antiskid system stops the airplane for all runway conditions in a
shorter distance than is possible with either antiskid off or brake pedal
modulation.
[...]
Braking with Antiskid Inoperative
When the antiskid system is inoperative, the following techniques apply:

ensure that the nose wheels are on the ground and the speedbrakes are
extended before applying the brakes
initiate wheel braking using very light pedal pressure and increase
pressure as ground speed decreases
apply steady pressure and DO NOT PUMP the pedals.

(Boeing 737 NG FCTM 6.45 - Landing, emphasis mine)
As you can see from the above quote, you will increase the stopping distance compared to a normal braking with anti-skid, which results in a larger accelerate-stop-distance, which then reduces the balanced field length V1.
It has nothing to do with the brake energy limitation because the maximum energy that can be absorbed by the brakes is the kinetic energy of the aircraft at the moment you start braking. It does not really depend on how you brake, but with anti-skid inoperative there is a chance that the tires will lock up while decelerating which actually reduces the amount of energy going into the brakes and increases the energy that goes into the tires (in the worst case, this energy will then cause a tire blowout).

It's generally a given that tires will be blown if any sort of hard high speed braking is attempted with AS off.  It's impossible to modulate the pressure with any accuracy to get close to lockup without going over.

with inop anti- skid, application of full brake press may result in wheel lock, skid and aquaplaning in certain situations. ineffective braking would entail larger distances : TORR (Take off) or ASDR (reject take off). for the same field length, temp, elev and AUW you have to reduce v1/vr ratio which would in turn reduces V1. this is for safely stopping the aircraft in case of reject take off within the ASDA.


text:
Why is Heraklion airport a 'captains only' airport?
I was recently watching "EasyJet: Inside The Cockpit" and it said pilots need 4 shoulder stripes to land at Heraklion International Airport, “Nikos Kazantzakis” (IATA: HER, ICAO: LGIR), but it didn't explain why they need the extra experience. Could someone please explain?

Oh, and since I happen to talk to ATCOs of Heraklion airport, it is a demanding airport because of the mountainous terrain surrounding the airport. But needing some specific piloting skills to land? Never heard of it.

Because 4-striped pilots can read and write and add and subtract?

I've always wondered on "captains only" rules what happens with a captain who has never flown into that airport before vs an FO who has been there many times.

Like a lot of things on the TV programme it was glossed over and out of sequence.
It is captains only due to terrain, weather, circling 09, lighting or lack thereof, upslope.
Here are the threats listed in the easyJet pilot notes:

Distractions during high workload visual approaches (this can mean checklist items are missed).
Visual illusions lead to PITCH alerts and firm landings due to low level environmental conditions.
RWY is upslope (causing ground rush effect), and there are variable RAD ALT callouts.
There are no approach lights on RWY27 as the approach is over the sea, this creates a “black hole” effect which is exacerbated by any further downgrade of the lighting.
Turbulence and downdrafts are common.
Taxiways Delta and Golf for RWY27 departures are not well illuminated and are easy to miss.
The final approach to RWY09 is made over the town; there is a church 250 m short of the RWY and the considerably displaced threshold; no instrument approach is published. Expect to circle from an approach to RWY27 or take vectors to a visual left base.

On most days this is a simple destination but there are potentially multiple tricky things so it is considered less risky to always have the captain perform the landing.

Heraklion is regularly included in a list of the Scariest/Most challenging/Unique (pick your adjective) runways in the world.
Most in this list are obvious why they feature. For example:

The airport at Courcheval in the French Alps has a steep runway, with a gradient of 18%, a length of just 1700 ft. and a vertical drop at the end

and

Also known as Lukla, the Himalayan airport is renowned for having one of the most feared runways in the world. Built on a steep incline in the middle of the Himalayan Mountains, it’s a mere 1500 ft. long and 65 ft. wide!

There is no obvious reason why Heraklion would be included. Today it is not a particularly short or narrow runway, it has many thousands of movements per year and is the second most busy airport in Greece.
It is a military airbase, and as such there could be frequent military movements, which could mean frequent diversions of civilian air traffic - but there is no particular evidence of this that I could find. A quick look at satelite imagary shows the runway in the proximity of mountainous terrain, but nothing which appears to require particularly complex routing on approach/final.
All in all I would say this is the usual kind of embellishment with entertainment shows regarding Aviation (Just last week on this show - Stalling: When the engine stops! My eyes nearly rolled back into my head).
A "4 stripe pilot" usually just means that he/she holds the rank of Captain for the airline. Its pretty standard fare to have a "4 star pilot" on board most flights.

BTW I got my quotes from this page: http://www.airportspotting.com/scary-runways-world/ read all the entries and try to work out why HER is even there. I can't.